This invention is generally directed to processes for affecting the preparation of colored toner compositions, and more specifically the present invention is directed to processes for affecting the preparation of colored toner compositions of a negative or positive polarity by dispersion polymerization. In one embodiment of the present invention the colored toner particles are generated by the dispersion polymerization of a mixture of monomer and attached steric stabilizer, and thereafter diffusing a dye solution into the polymerized product. Subsequently, dry, colored, xerographic toners are isolated by, for example, spray drying or freeze drying of the resulting dispersions. The triboelectric properties of the toners obtained in accordance with the aforementioned process are controlled by the steric stabilizer anchored on the surface thereof. Therefore, strongly positive charging colored toners are obtained when stabilizers such as poly(vinylpyridine), poly(ethyleneoxide), and cellulosic derivatives are selected; while negatively charged colored toners are generated with steric stabilizers such as poly(acrylic acid), poly(styrene sulfonic acid), copolymers thereof, and poly(maleic anhydride) copolymers. Additionally, the stabilizers selected inclusive of hydroxypropyl cellulose can be reacted with other compounds for the purpose of transforming the surface sites thereby permitting modification of the charge on the toner composition. The resulting transformed stabilizers are thus functioning in a manner similar to known charge enhancing additives. Toner compositions obtained in accordance with the process of the present invention are useful for causing the development of images in electrostatographic imaging methods, particularly colored electrostatic imaging methods wherein the imaging members selected can be positively or negatively charged.
Polymerization processes for obtaining black toner compositions are well known. There is thus disclosed in U.S. Pat. No. 4,282,304 a suspension polymerization method wherein magnetic particles are initially mixed with monomer together with an initiator, and subsequently this mixture is suspended in an aqueous medium wherein a reaction occurs within each particle resulting in the formation of particles of the size needed for use as toner compositions. The particles obtained are removed from the aqueous medium by various known techniques inclusive of evaporation. Stabilizing compounds selected for the process of this patent include methyl hydroxypropyl cellulose, and other similar materials; however, these stabilizers are not believed to be permanently attached to the polymer product resulting.
There is also disclosed in copending application Ser. No. 553,598, entitled Ink Jet Compositions and Processes for Preparation, the disclosure of which is totally incorporated herein by reference, microsuspension processes for the preparation of particles for ink jet printing which comprises providing a monomer having dissolved therein an oil soluble dye followed by mixing with the resulting monomer particles polymer initiator compounds. Thereafter, the solution generated is mechanically mixed and there is added thereto water and surfactant agents followed by subjecting the solution resulting to ultrasound vibrations. Subsequently, the aforementioned solution is heated to a temperature of about 50.degree. C. to about 100.degree. C. causing polymerization, enabling polymer particles containing therein oil soluble dyes stabilized by surfactant particles; and wherein these particles are of a diameter of from about 0.03 micron to about 2.0 microns.
Moreover, described in a copending application Ser. No. 549,933, entitled Stable Polymeric Dispersion and Methods for Making, the disclosure of this application being totally incorporated herein by reference, are stable polar dispersions with non-ionic amphipathic steric stabilizers irreversibly anchored to a monomer compound. Stabilizers disclosed in this application include graft copolymers of cellulose compounds such as hydroxyethyl cellulose.
Additionally, positively charged toner compositions are known, reference for example U.S. Pat. No. 3,893,935, which discloses the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. Furthermore, there is disclosed in U.S. Pat. No. 4,338,390 positively charged developer and toner compositions prepared by melt blending and having incorporated therein as charge enhancing additives organic sulfate and sulfonate compounds. Similarly, disclosed in U.S. Pat. No. 4,298,672 are positively charged toner compositions comprised of resin particles, and pigment particles; and as charge enhancing additives, alkylpyridinium compounds and their hydrates. Other prior art disclosing toner compositions with charge control additives therein include U.S. Pat. Nos. 3,944,493; 4,007.293; 4,079,014; and 4,394,430.
An important disadvantage associated with conventional methods of preparing toner compositions, inclusive of melt blending, is that the charge directing additive is introduced into the toner resin during processing with the pigment particles undesirably causing most of the additive to be entrained in the core of the toner particle. Accordingly, the entrapped additives, unless present in excessive amounts, cannot substantially influence the charging properties of the resulting toner particles. Also, with many prior art processes toner particles with a diameter of below about 10 microns cannot readily be generated without effecting the removal of large quantities of fines. Additionally, in the prior art toner processing inhomogeneities in the pigment dispersion can sometimes occur during the melt blending operation resulting in opacity when, for example, such a toner is selected for the preparation of transparencies. The dispersion polymerization process of the present invention substantially eliminates these difficulties.
There is thus a need for generating colored toner compositions by dispersion polymerization processes. More specifically, there remains a need for generating colored toner compositions of selected polarities, that is, either a positive polarity or a negative polarity with dispersion polymerization processes by affecting a chemical attachment of the stabilizer selected. Moreover, there continues to be a need for generating positively charged or negatively charged colored toner compositions which can be prepared in a simple and economical manner; and wherein the resulting charge enhancing additive moiety is retained and not leeched from the toner as is the situation with several prior art charge enhancing additives. Additionally, there continues to be a need for generating color toner compositions of an appropriate size diameter of from 5 to 20 microns; and wherein the charge enhancing additive function is assumed by the stabilizer compounds selected for the dispersion polymerization process. There is also a need for dispersion polymerization processes wherein the resulting color toner compositions are of monodispersed particle size distributions; and wherein the colorant selected is molecularly dissolved within the toner particles with exceptionally high desirable homogeneity. Further, there is a need for obtaining colored toner compositions by dispersion polymerization processes wherein the charge directing compound, that is the stabilizer, is chemically and permanently anchored on the surface of the toner particles. Also, there is a need for obtaining colored xerographic toners by dispersion polymerization processes enabling the compositions resulting to possess a lower fusing temperature.